A fuel cell is a power-generating unit that generates electrical energy through electrochemical reaction of hydrogen-containing fuel and air. Since the fuel cell has the advantages of low pollution, high efficiency, and high energy density, it has been positively researched, developed, and promoted in many countries. Among others, the proton exchange membrane fuel cell (PEMFC) is the most industrially valuable product due to its low operating temperature, quick activation, and high energy density.
In the fuel cell, hydrogen ions move from the anode to the cathode to complete the electrochemical reaction. The performance of a fuel cell has close relation to different operating conditions, such as temperature, humidity, hydrogen flow, air flow, etc. Regarding the humidity, it is necessary to keep a high molecular proton exchange membrane in the fuel cell at proper operating humidity for the fuel cell to achieve high performance. Meanwhile, the fuel cell must also be maintained at a proper operating temperature.
To maintain the fuel cell at proper operating humidity and temperature, one of the currently adopted ways is to provide the reactant gas supply pipelines of the fuel cell with a humidifier associated with a cooling water system. With this arrangement, cooling water is supplied from the cooling water system to cool the fuel cell and then discharged from the fuel cell. The discharged cooling water has a high temperature about 60 to 70°C., and is led to the humidifier to increase the humidity and temperature of the reactant gas passed through the humidifier before the reactant gas is supplied to the fuel cell. For example, fresh air or oxygen is sent by an air blower to the humidifier before being led to the fuel cell via an oxygen inlet port thereof, so that the air flown into the fuel cell has a proper humidity.
While the technique of providing a humidifier to regulate the humidity of the reactant gas for the fuel cell has become matured, there is not any technical teaching or suggestion on using a humidifier to treat the unreacted gas discharged from the fuel cell.
Another important issue about the fuel cell is the unreacted hydrogen discharged from the fuel cell. Unlike the unreacted oxygen that can be directly discharged into ambient air, the unreacted hydrogen is highly dangerous and subject to self-combustion and explosion when a local concentration of the discharged unreacted hydrogen exceeds 4%. Therefore proper measures must be taken to treat the unreacted hydrogen discharged from the fuel cell. In a currently adopted way, the unreacted hydrogen is led back to the fuel cell and recycled. However, the recycled hydrogen as reactant gas has reduced purity to possibly cause the poisoning problem. One way to solve the above purity and poisoning problems is to recycle only part of the discharged unreacted hydrogen. The remaining part of the discharged unreacted hydrogen is led to a catalytic converter and treated before being discharged into ambient air. However, the catalytic converter requires additional and quite high cost.